1. Field of the Invention
This invention relates to an improvement in percutaneous transluminal angioplasty, which improvement permits the removal of plaque material from a vas.
2. Description of the Prior Art
It is known that artherosclerotic plaque tends to form in a vas, such as an artery, of a large number of people. Such plaque on the wall of a vas, which partially occludes the lumen or channel of the vas, may occur in coronary blood vessels or in peripheral blood vessels. In the case of coronary blood vessels, the reduced blood flow caused thereby results in chronic heart problems, including miocardial infarction. The narrowing of the lumen of peripheral blood vessels, such as an artery of the leg, by the partial occlusion thereof by artherosclerotic plaque is also a recognized problem.
One of several known treatments for the partial occlusion of the lumen of a vas by artherosclerotic plaque, is percutaneous transluminal balloon catheter angioplasty. This method involves insertion of a deflated balloon into the lumen of an artery that is partially obstructed by plaque, and then inflating the balloon in order to enlarge the lumen by means of pressure exerted by the inflated balloon on the plaque. More specifically, the initial existence of protuberance of plaque in a vas acts as a bottleneck that severly restricts the flow of blood. The plaque protuberence is squeezed by the balloon, thereby causing deformation and smoothing of the shape of the plaque surface that substantially eliminates the protuberance, thus enlarging the lumen. In order to make the plaque deform more easily, the plaque may be softened somewhat by heat applied thereto. In this regard, reference is made to U.S. Pat. No. 4,643,186, which issued to Rosen et al. on Feb. 17, 1987, and is entitled "Percutaneous Transluminal Microwave Catheter Angioplasty" This patent discloses the use of radio-frequency or microwave frequency electrical energy radiated from an antenna within the interior of a balloon catheter into a plaque protuberence to heat and soften the plaque material so that the plaque material is more easily deformed and smoothed by the pressure exerted by the balloon portion of the catheter.
Regardless of whether or not the plaque material is softened by heat, a mere deformation in the shape of the plaque material, within the vas, and not in the removal from the vas of any of the mass of the plaque material: results in the bore of the treated vas being narrower than it would be if, in addition to the smoothing of the surface of the plaque, at least a portion of the mass of the plaque material were removed from the vas.
Although somewhat dangerous, it becomes necessary at times, in performing percutaneous transluminal balloon catheter angioplasty as is presently practiced, to apply sufficient pressure on the wall of a vas, such as an artery to break the surrounding arterial muscle in order to achieve a significant widening of the lumen of the artery.
Another technique which has recently received a good deal of attention is transluminal laser catheter angioplasty. This treatment involves introduction into the coronary artery of a fiber optic cable the proximal end of which is connected to a laser energy source. The distal end of the fiber optic cable is directed towards the plaque. The laser is pulsed, and the resulting high energy light pulse vaporizes a portion of the plaque. Many problems remain unsolved in laser catheter angioplasty. Locating the plaque requires some means such as a fiber optic scope to see the region towards which the laser pulse will be directed. The interior of the artery must be illuminated, and a clear liquid introduced into the artery to displace opaque blood from the region to be viewed. Even with a fiber optic scope, however, the plaque may be difficult to distinguish from normal arterial walls. When the energy of the laser discharge is directed towards the arterial walls, the walls may undesirably be perforated. Further problems related to the difficulty in matching the characteristic of lasers and fiber optic cables to the frequency absorption characteristics of various types of plaque, and the by-products of the destruction of the plaque.
The present invention makes it possible to use percutaneous transluminal balloon catheter angioplasty to more safely remove plaque material from the vas than is the case with transluminal laser catheter angioplasty.